This invention relates generally to systems and methods for verifying identity of people, by comparison and interpretation of skin patterns such as fingerprints; and more particularly to novel firmware and software stored in apparatus memories, as portions of apparatus, for interpreting such patterns and controlling utilization devices. With respect to certain of the appended claims, the invention further relates to systems that include such utilization devices.
A utilization device is, for example, a facility, apparatus, means for providing a financial service, or means for providing information. The phrase xe2x80x9cutilization devicexe2x80x9d thus encompasses, but is not limited to, businesses, homes, vehicles, automatic teller machines, time-and-attendance systems, database-searching services, and a great many other practical systems. An apparatus memory for such storage is, for example, a programmable read-only memory (xe2x80x9cPROMxe2x80x9d), or a computer-readable disc.
Classical methods for evaluation of fingerprints. toeprints, palmprints and like skin patterns entail location, categorization and tabulation of minutiae. Efforts to adapt these classical techniques for automated print verification have received great attention and elaboration, but are fundamentally limited by their sensitivity to measurement noise at the location of the minutiae.
Automated analysis based on minutiae also is inherently very dependent on image enhancementxe2x80x94which often breaks down when initial data quality is marginal. For these reasons some workers have explored other methodologies.
Some seemingly promising efforts employ hologramsxe2x80x94either direct three-dimensional images of prints, or holographic Fourier transforms (which have the advantage of being position invariant). Some of these techniques, for best results, impose costly demands on special memory devices for storing the holograms. These holographic correlators are in essence modern refinements of much earlier two-dimensional direct-optical-overlay correlators such as that described by Green and Halasz in U.S. Pat. No. 3,928,842.
An intermediate ground is represented by a few relatively sophisticated patents that use digital computers to (1) automatically select one or more distinctive small regionsxe2x80x94not necessarily minutiaexe2x80x94in a master print or xe2x80x9ctemplatexe2x80x9d, and then (2) automatically look for one or more of these selected small regions in a print provided by a person who purports to be the maker of the template. These earlier patents particularly include U.S. Pat. No. 5,067,162 of Driscoll, U.S. Pat. No. 5,040,223 of Kamiya, U.S. Pat. No. 4,982,439 of Castelaz, U.S. Pat. No. 4,805,223 of Denyer, and U.S. Pat. No. 4,803,734 of Onishi.
All of these latter patents describe making final verification decisions based upon such comparisons of small regions exclusivelyxe2x80x94although in some cases a small number of such regions are considered concurrently. We have confirmed that many fingerprints can be analyzed very quickly and accurately using just one or two regions, but we have also found that provision must be made for a significant number of prints in which such short-form efforts are indeterminate or at least not adequately reliable.
Thus the patents listed just above are flawed in their ultimate dependence upon isolated, small amounts of dataxe2x80x94more specifically, very small fractions of the available information in a candidate user""s printxe2x80x94for all fingerprints, regardless of the character of the print. The above-mentioned related patent document of Thebaud, on the other hand, takes into account essentially all the available information in a candidate print.
Thebaud""s system does so for all prints. We have recognized that for some types of systems this thoroughness and the accompanying time consumption can represent a significant drawback, becausexe2x80x94in a large majority of casesxe2x80x94small regions contain sufficiently distinctive information for a reliable analysis.
Some of the patents in the above list do describe sound techniques for one or another part of their respective processes. Some workers, such as Driscoll and Kamiya, use correlation methods (but electronic-data correlation methods, not optical correlation methods) to choose the small reference sections in the enrollment processxe2x80x94i.e., in forming the templatexe2x80x94and also in comparison of those regions with features in a candidate user""s print. Denyer similarly uses an approximation to such correlation technique.
These patents do generally allow for the possibility that the authorized user""s template may be shifted, or in other words translated, in placement of the print image on the sensor. Some (particularly Driscoll and Denyer) allow for the possibility that the template may be rotated too.
Driscoll discusses finding a least-squares-fit between plural reference regions and a potentially corresponding plurality of test regions in the candidate print. He suggests that departures from an ideal rotated pattern of the reference regions is to be accounted for by distortion of the fingertip in the course of placement on a sensor, but by his reliance on a very small number (typically three, as understood) of well-separated reference regions his allowance for distortionxe2x80x94and his overall verification decision as wellxe2x80x94inherently make use of only a very small fraction of the available information. Denyer, too, briefly mentions (though in a much more generalized and tangential way) the possibility of somehow accounting for distortion.
All of these patent documents except Thebaud""s, however, fail to take account of dilations which an authorized user""s fingertip may undergoxe2x80x94relative to the same user""s established template. (By the term xe2x80x9cdilationsxe2x80x9d we mean to encompass dilations or contractions as the case may be.) Such dilations may arise from variations in the pressure with which the finger is applied to an optical or other sensor (capacitive, variable-resistance etc.).
Such dilations may be expected to have at least a component which is invariant across the entire image, in other words a dilation without change of fingerprint shapexe2x80x94an isomorphic dilation. Furthermore all the above-mentioned patents fail to make systematic, controlled allowance for dilations and other forms of distortion that are differentialxe2x80x94which is to say, nonisomorphic.
Correlation methods, matched-filter methods, and (loosely speaking) related overlay-style techniques of comparison all fail totally in any area where a reference print is mismatched to a candidate print by as little as a quarter of the spacing between ridges. It has been found that dilations and other distortions can and commonly do produce spurious mismatches locallyxe2x80x94over sizable areasxe2x80x94exceeding twice the spacing between ridges, that is, many times the minimum disruption which destroys correlation and thereby recognition.
Therefore, failure to account properly for either dilation (isomorphic distortion) or distortion (differential distortion) results in unacceptably high rates of failure to verify or recognize an authorized userxe2x80x94i.e., high rates of the so-called xe2x80x9cfalse rejectionxe2x80x9d or xe2x80x9ctype 1 errorxe2x80x9d. Artificial measures aimed at reducing this failure rate lead inevitably to the converse: unacceptably high rates of failure to reject unauthorized users, impostorsxe2x80x94i.e., high rates of the so-called xe2x80x9cfalse acceptancexe2x80x9d or xe2x80x9ctype 2 errorxe2x80x9d.
For those few cases in which abbreviated analysis is unreliable, it appears unlikely that adequate account of distortions can be made merely by allowing for random variation as between two or three cores or distinctive regions. The full-coverage paradigm of the Thebaud document, by virtue of its ability to use all information available in the entire area of overlap between the reference and test images, has an immunity to such error, but at the cost of a relatively long analysis timexe2x80x94currently several seconds (after the fingerprint data are fully acquired) per determinationxe2x80x94even for prints which have very distinctive regions.
Similarly none of the prior-art patents noted makes use of decisional downweighting of data from areas that are less certain or noisier; rather, to the extent that any consideration at all is given to such matters, noisy data are simply discardedxe2x80x94a very undesirable way to treat expensive data. Bandpassing of test data is not seen in these references, although certain other forms of filtering are used by Driscoll and others. Normalizing is likewise absentxe2x80x94except for trivial forms implicit in binarization or trinarization, used in many print analyzers. None of the noted patents teaches expression of test and template data, or comparison of such data with one another, in terms of local sinusoids.
Another problem which the art has not adequately addressed heretofore is that of image-data coverage and quality. It is common in commercial devices in this field to find that images are acquired and accepted for analysis based only upon occluding of the acquisition port by a finger or some other objectxe2x80x94i.e., the presence of something at the acquisition portxe2x80x94without regard for the usability or reliability of the image, or indeed even whether it is an image of a fingerprint or other skin pattern.
Still another difficulty is that analysis systems are not necessarily attuned to the peculiarities of the skin-pattern data encountered. When analysis proceeds on assumptions (for example, the size of the fingerprint-ridge spacing) that are not applicable to the actual specimen presented, reliability of the results is impaired.
Another challenge not adequately met heretofore is that fingerprint acquisition systems labor under severely adverse conditions of low skin-pattern contrast and high variation in lighting across the patternxe2x80x94so that a relatively high dynamic range in light intensities is presentxe2x80x94but yet the cost, time consumption and in some cases sheer space and bulk required to store or transmit the resultant, correspondingly high-dynamic-range signal data.
A very closely related problem is that attempts to reduce the required cost, time consumption and space or bulk associated with data storage and transmission run into a contrary requirement that the data must be fairly comparable to original data. It must not have anomalous characteristics that can be associated with, for example, commonplace data-compression techniques. A particularly knotty problem is the need for smoothness along ridges, lest the analysis system be unable to recognize their essentially continuous character.
Thus the skin-pattern verification field has failed toxe2x80x94in a time-effective mannerxe2x80x94make good use of all available data, take adequate account of dilations or distortions, make suitable allowance for known statistics of placement variation, and apply modern decisional and signal-processing tools. As can now be seen, prior art in this field remains subject to significant problems, and the efforts outlined abovexe2x80x94while praiseworthyxe2x80x94have left room for considerable improvement.
The present invention introduces such improvement, and performs fingerprint verifications in a remarkably short time and with an outstandingly high accuracy not available heretofore. The invention has several facets or aspects which are usable independentlyxe2x80x94although for greatest enjoyment of their benefits we prefer to use them together, and although they do have some elements in common.
Common parts will be described first. In preferred embodiments of the first three independent facets which will be discussed below, the invention is apparatus for acquiring personal skin-pattern print data for use in comparison to verify the identity of a person.
In preferred apparatus embodiments of the next seven independent facets to be discussed (i.e., the fourth through tenth aspects), the present invention is apparatus for verifying the identity of a person. It operates by comparing (1) test data representing a two-dimensional test image of that person""s skin-pattern print with (2) reference data derived from a two-dimensional reference skin-pattern print image obtained during a prior enrollment procedure.
Certain additional aspects or facets of the invention will be described following the first ten. Each of the apparatus embodiments includes some means for holding instructions for automatic operation of the other elements of the apparatus; these instruction-holding means include or make use of a nonvolatile memory device, and may be termed the xe2x80x9cnonvolatile memory meansxe2x80x9d.
Now in preferred embodiments of a first of its independent aspects, the apparatus includes some means for physically receiving contact by the skin of such a person and for, during that contact, forming an optical image of the skin pattern. For purposes of breadth and generality in discussion of the invention we shall refer to these means simply as the xe2x80x9coptical meansxe2x80x9d.
In addition the apparatus includes some means for receiving the optical image from the optical meansxe2x80x94and generating in response a series of electronic signal arrays derived from such pattern during the contact. Again for generality and breadth we shall call these the xe2x80x9coptoelectronic meansxe2x80x9d.
In addition the apparatus includes some means, the xe2x80x9celectronic meansxe2x80x9d, for monitoring the series of electronic signal arrays during the contact; and some means, the xe2x80x9csaving meansxe2x80x9d, for saving at least one of said electronic signal arrays for use in such comparison. Also in the apparatus are some means for deferring operation of the saving means until at least one of the electronic signal arrays in the series satisfies a particular condition related to a characteristic of the pattern; these last xe2x80x9cdeferring meansxe2x80x9d are responsive to the electronic monitoring means during the contact.
The foregoing may represent a definition or description of the first aspect of the invention in its broadest or most general form; however, even in this form this facet of the invention can be seen to importantly advance the art of fingerprint acquisition and analysis. In particular the system is more reliable than heretofore, in that an image is accepted for analysis only if its quality (and as will be seen its areal coverage) are adequate for analysis.
Nevertheless we prefer to practice the first aspect of the inventionxe2x80x94and others mentioned below as wellxe2x80x94with certain further features and characteristics that enhance enjoyment of the benefits of the invention. Accordingly we prefer, for example, that the xe2x80x9cparticular conditionxe2x80x9d mentioned above includes a test for adequacy of skin-pattern image area, based not merely upon occlusion of the optical data port but actually upon spatial-frequency content of the electronic signal arrays.
That is to say, the signals should contain energy at spatial frequencies characteristic of skin-pattern prints, even when our invention is simply testing for areal coverage. A like more but stringent criterion is applied when the system is at a more advanced stage of testing for quality of the print.
Furthermore we have found that details of a skin contact settle during contact, and the electronic signal arrays in the series tend to improve as said skin contact settles. We accordingly prefer to collect sequential images over an extended period of time when necessary, halting the process only if and when an image is acquired that passes usability criteria.
Numerous other preferences will appear in regard to this first aspect (and the others as well) of the invention, in the xe2x80x9cDETAILED DESCRIPTIONxe2x80x9d section that follows.
In preferred embodiments of a second main facet or aspect of the invention, the apparatus includes some means for receiving or generating an electronic signal array corresponding to the skin patternxe2x80x94these will be called the xe2x80x9creceiving or generating meansxe2x80x9dxe2x80x94and also some means for defining a plurality of signal wavenumber bands.
Included moreover are some meansxe2x80x94the xe2x80x9ccomparing meansxe2x80x9dxe2x80x94for comparing wavenumber content of the electronic signal array with the plurality of defined wavenumber bands. Further the system includes some means for selecting a particular one band of said plurality to use in analyzing said electronic signal array to verify the identity of such person; these selecting means are responsive to the comparing means.
Even as defined thus broadly, a system in accordance with this second aspect of our invention operates in a signal spatial waveband that is specifically chosen to match the data encountered. Reliability of the resulting analysis is accordingly enhanced.
In preferred embodiments of the third main aspect of the invention, the apparatus include some means for receiving or generating a multilevel electronic signal array corresponding to such skin pattern. It also includes some means for preliminarily evaluating or preprocessing, or both, the multilevel electronic signal array.
By xe2x80x9cmultilevelxe2x80x9d we mean that the dynamic range of the signal is at least four binary bitsxe2x80x94i.e., a factor of sixteen times the smallest signal shift which the system can comprehendxe2x80x94and preferably five bits or more. Our present preferred embodiment is an eight-bit system, though this is primarily a matter of economically available components.
In addition the apparatus includes some means for expressing the preliminarily evaluated or preprocessed, or both, signal array in two- or one-bit form. It also includes means for storing or exporting the signal array expressed in said two- or one-bit form.
The foregoing may provide a definition or description of the third aspect of the invention in its most general or broad form, but even as thus broadly couched the third aspect of the invention significantly advances the art. In particular, preferred embodiments according to this third facet of the invention can now be seen to provide a full dynamic range for the signal, to allow for lighting variationsxe2x80x94and other variables such as whether the skin-pattern contrast is high or low. At the same time this aspect of the invention does not compromise as to the time, space or cost of storage or data-export capacity.
As mentioned earlier, several preferences are applicable to even still further enhance the benefits of this third aspect of the invention.
As to the fourth main aspect of the invention, the apparatus includes some means for extracting reference data from storage or from an imported data set for use in verification. The apparatus also includes preprocessing means for bandpassing, normalizing and smoothing the extracted data for use in verification.
Further included are some means for comparing the data from the preprocessing means with the test data to verify identity. The foregoing presentation may represent the fourth facet of the invention in its most broad and general manifestation, but even so it does meaningfully promote the art, particularly in that economically and quickly exported or stored data with only one or two bits (in accordance with the third aspect of the invention) is readily and economically rendered completely adequate for use in analysis.
Turning to a fifth major facet of the invention, the apparatus includes some means for deriving from reference data or test data, or both, a respective form of a vector gradient field. The apparatus also includes some means for smoothing such reference or test data, or both, under control of the vector-gradient-field form so that the smoothing is substantially along the directions of respective ridges of the skin pattern. In addition the apparatus includes some means for applying the smoothed data in making an identity-verification decision.
In this way data quality needed for entirely reliable analysis is simply reconstituted, when stored or transmitted image information is readied for use. No compromise need be struck between storage/transmission economies and reliability of verification.
This broadest form of the fifth facet of the invention, too, is subject to additional preferences. For instance we prefer to find a vector gradient field from a fast Fourier transform of the data, screening the vector gradient field to account for phase jumps.
In addition, merely as a matter of practicalities we currently prefer that the form of vector-gradient-field employed be a vector wavenumber field. This preference arises simply from the availability of a finished routine for accomplishing this task, as our current most highly preferred form of the apparatus does not actually use the scalar magnitudes that are part of the wavenumber field.
We nonetheless prefer, in view of the availability just mentioned, that the deriving means further comprise some means for calculating from the gradient field a covariance matrix, and from the covariance matrix in turn a scalar magnitude field for the wavenumber. In this case we also prefer that the system include some means for constructing the vector wavenumber field as the scalar magnitude field with directedness of said vector gradient field.
In preferred embodiments of yet a sixth main facet or aspect of the invention, the apparatus includes some means for computing power spectral density of at least a portion of the test image. In addition it includes some means for applying the power spectral density to estimate an assumed dilation of the test image relative to a reference image.
Also the apparatus includes some means for comparing the test data with the reference data, taking into account the estimated dilation. Further included are some means, responsive to the comparing means, for making an identity-verification decision.
The foregoing may represent the sixth main aspect of the invention in its most broad or general form. Even as thus formulated, however, this facet of the invention provides an extremely important contribution to the art of fingerprint and other skin-pattern-print analysis.
As will be explained in greater detail later in this document, power spectral density (or xe2x80x9cPSDxe2x80x9d) can be made to reveal both the spacing and directionality of skin-pattern ridgesxe2x80x94particularly within a small area of a pattern. By comparing the spacing portion of a PSD for a test image with the like portion of a PSD for a reference image or xe2x80x9ctemplatexe2x80x9d, the present invention is thus able to read off the relative dilation of a test image relative to a reference image, for corresponding areas.
In this way, as will shortly be seen, the invention produces excellent approximations to the results of not only the early global search of the Thebaud patent document but also the later gradient search with its holistic nonisomorphic distortion fields. The PSD technique, once systematized and made efficient, also can be used for screening prints at acquisition to be certain that energy is present in spatial wavebands characteristic of skin-pattern prints.
A calculation of two PSDs, however, unlike the time-consuming procedure taught by Thebaud, for a small region takes a very small fraction of the time which his apparatus requiresxe2x80x94most typically between one and two orders of magnitude faster overall. Thus the present invention is able to achieve very nearly the same results in considerably less than a tenth the time.
In preferred embodiments of a seventh of its major aspects, the invention is closely related to that of the sixth but with respect to rotation rather than dilation. Once again a good estimate of relative rotation is accomplished merely by comparing the orientational portion of a test-image PSD with the corresponding portion of a reference-image PSD.
Through finding both the relative dilation and rotation in this way, the invention is able to estimate the entire isomorphic distortion with surprising accuracy. Through use of a multiple set of regions covering a full print area, or at least the area of overlap between reference and test images, the invention also approximates adequately the nonisomorphic distortions found by Thebaud.
Preferred embodiments of an eighth main aspect of the invention are also related to analysis by PSD comparisons. The apparatus here includes some means for computing power spectral density of at least a portion of the test image and of the reference image, respectively.
In this main facet of the invention, the apparatus also includes some means for transforming the respective computed power spectral densities to polar coordinates. Through this innovative tactic, the transformed power-spectral-density informationxe2x80x94which now can be interpreted as rectangular-coordinate dataxe2x80x94has the form of power-density values plotted on a rectangular grid of ridge spacing and orientation.
In addition the apparatus includes means for considering the transformed power spectral densities for such test and reference images together. These means also have the further function of reading off from the xe2x80x9cconsidered-togetherxe2x80x9d power spectral densities an estimate of such assumed relative rotation and dilation.
The particularly favorable result, in the case of this eighth aspect of the invention, is that even greater time savings and efficiency can be gained by expressing the ridge orientation and spacing as fields defined within the same rectangular grid and rectangular-coordinate mathematics as are applicable to most of the other procedures in the fingerprint analysis. All these advantages are further enhanced by preferred operating modes such as ratioing the respective ridge-spacing and orientation values, or correlating the two transformed power spectral densitiesxe2x80x94within a hypothesis range of relative rotation and dilationxe2x80x94to find an estimate of the most probable relative rotation and dilation.
In preferred embodiments of a ninth of the main aspects or facets of the invention, the apparatus includes some means for estimating relative translation, and at least one component of relative isomorphic distortion, between the test and reference images. It also includes means for adjusting the test or reference image, or both, to allow for the estimated relative translation and component of relative isomorphic distortion.
Further the apparatus includes some means for comparing the test and reference images, after the adjustment, within substantially all area that is common to both images, to make an identity-verification decision. As will be noted, this advantageous operating scheme is in common with the invention set forth in the previously mentioned Thebaud patent documentxe2x80x94and represents a potent advance over the prior art.
We prefer, however, to practice this ninth aspect of the invention in conjunction with certain other facets or aspects that maximize enjoyment of the benefits of the invention. For example we prefer that the comparing means include means for analyzing power spectral densities within the common area to estimate remaining distortions.
In this regard we prefer that the comparing means include some means for dividing one of the images into a multiplicity of substantially overlapping subregions that in the aggregate cover substantially the entire said one image; and additional means for evaluating the degree of similarity of said test and reference images, with respect to substantially every one of said subregions of which a significant fraction is within said all area common to both images.
In this way the capability of the PSD to yield rotation and dilation information very quickly and efficiently for small areas is exploited to obtain an estimate of such information for quite large areas. Preferably the evaluating means include some means for estimating, within each of the subregions in the common area respectively, a further component of relative distortion between test and reference images.
Preferably evaluating means form a composite measure of the xe2x80x9cfurther componentsxe2x80x9d for all of said subregions in the common area; and means for thresholding that composite measure to make said decision. Also preferably the apparatus extracts from the test data an estimate of noise variance in the test data as a function of position in the test image; in this system the composite-measure forming means take into account the estimated noise variancexe2x80x94and preferably weight the further component of distortion, for each of the subregions in the common area, in an inverse relation with the noise-variance estimate for that subregion.
In preferred embodiments of yet a tenth major aspect of the invention, the apparatus includes some means for comparing a first small region of the reference data with the test data to form a first measure of similarity. It also includes first means for testing that first measure against a first threshold to verify such person""s identity.
In case the first measure is not high enough for acceptance, the apparatus also includes some means for then comparing a second small region of the reference data with the test data to form a second measure of similarityxe2x80x94and associated second means for testing said second measure against a second threshold that is higher than the first threshold, to verify such person""s identity. As will be noted, it would be more expectable after failure of the first measure to test against a second measure that is lower, but that is not the case in the tenth major aspect of the present invention.
The reason for this anomaly is that the second test employs a smaller window. This strategy is adopted on the basis of the reasoning that the first test may have failed in recognition merely because too much distortion is present to allow recognition over the area of the first test: it is a small area, but that of the second test is relatively even smaller.
Several other preferences will appear. In particular, the first testing means also test the first measure of similarity against a first, relatively low, rejection threshold to deny verification. The second comparing means operate only if the first measure of similarity is between the first acceptance and rejection thresholdsxe2x80x94i.e., if the first measure of similarity is neither high enough for acceptance nor low enough for rejection.
Preferably the second testing means also test the second measure of similarity against a second rejection threshold that is higher than the first rejection threshold, to deny verification. As noted above, the second small region is smaller than the first small region.
Also preferably, in event the second measure is between the second acceptance and rejection thresholdsxe2x80x94so that the second measure is neither high enough for acceptance nor low enough for rejectionxe2x80x94then the system compares substantially the entire common area of the test and reference images to make a verification decision.
Preferred apparatus embodiments of yet an eleventh independent facet or aspect of our invention diverge somewhat from the first seven. The apparatus here is for receiving surface-relief data from a sensor that acquires surface-relief data from a relieved surface such as a fingerxe2x80x94and in response controlling access to facilities, equipment, a financial service, or a system for providing or receiving information.
The apparatus is for use in the presence of an assumed dilation of the relieved surface. The apparatus includes a system for processing the received data to determine identity of the relieved surface. In addition to the previously mentioned instruction-holding memory means, this system includes:
means for calculating and comparing power spectral densities of at least a portion of the received data and test data respectively, and analyzing the power spectral density comparison to estimate the assumed dilation,
means for comparing the test data with reference data, taking into account the estimated dilation, and
means, responsive to the comparing means, for making an identity-verification decision.
In addition, the overall apparatus includes some means for applying the determined identity to control access to such facilities, equipment, financial service, or source or reception of information. Thus this aspect of the invention, while specifically incorporating the dilation-estimating feature mentioned above in connection with the fifth independent aspect, particularly focuses on and includes, as part of the invention, components that actually control access to various types of utilization means.
A twelfth independent facet of the invention involves a further divergence, in that it is a secured system subject to access control based upon surface-relief data from a relieved surface such as a finger. This system is for use in the presence of an assumed distortion of the relieved surface.
The system includes utilization means, susceptible to misuse in the absence of a particular such relieved surface that is related to an authorized user. The utilization means being selected from the group consisting of:
a facility,
apparatus,
means for providing a financial service, and
means for providing or receiving information.
In addition the system includes sensor means for acquiring surface-relief data from such a relieved surface.
The system also includes some means for processing the data to determine identity of the relieved surface, and for applying the determined identity to control access to the utilization means. These processing and applying means include, in addition to the instruction-holding memory means:
means for calculating and comparing power spectral densities of at least a portion of the received data and test data respectively, and analyzing the power spectral density comparison to estimate the assumed dilation,
means for comparing the test data with reference data related to the particular relieved surface related to the authorized user, taking into account the estimated distortion, and
means, responsive to the comparing means, for making an identity-verification decision.
Thus this aspect of the invention includes the utilization means themselves, as well as the access-control intermediary that is included in the eighth aspect of the invention.
While thus focusing on and including the utilization means, the invention makes use of the distortion-estimating feature discussed earlier in connection with the sixth independent facet of the invention.
In yet another of its independent aspects or facets, preferred embodiments of the invention take the form of a method, rather than apparatus. This method is for verifying the identity of a person. The method does so by comparing test data representing a two-dimensional test image of that person""s skin-pattern print with reference data derived from a two-dimensional reference skin-pattern print image obtained during a prior enrollment procedure.
The method includes the step of ratioing or correlating power spectral densities of corresponding regions of the test and reference images to determine relative isomorphic distortion between the images. Another step is using a normalized spatial correlation value as a measure of similarity between corresponding regions of the test and reference images.
Furthermore the method includes the step of making an identity-verification decision based on said normalized spatial correlation value. Another step is, in nonvolatile memory, holding instructions for automatic operation of the foregoing steps.
Thus the method partakes of the advantageousness of the apparatus embodiments of the power-spectral-density aspects of the invention, discussed earlier. Preferably this method is optimized by incorporation of other features or characteristics, particularly the steps of operating a sensor to acquire the test data andxe2x80x94responsive to the decision-making stepxe2x80x94operating a switch if identity is verified.
All of the foregoing operational principles and advantages of the present invention will be more fully appreciated upon consideration of the following detailed description, with reference to the appended drawings, of which: